1. Field of the Invention
This invention relates to fittings for use in fastening to structural members of metal framing systems, and more particularly to such fittings for use in fastening to a channel-shaped member having a longitudinal slot, in a side and narrower than that side, through which an elongated threaded element may be passed and then rotated to engage the interior of the slot for fastening to the fitting. A metal framing system of this class, together with some typical fittings and fastenings, is set forth in U.S. Pat. No. 2,345,650 to Charles W. Attwood. The disclosure of that patent is incorporated herein by reference, as if set out at length.
According to conventional usage which has developed in the construction industry with respect to this kind of framing system, a "fitting", alternatively called a "connector" or a "bracket", is understood to be a stout and strong piece of stiff bent sheet metal which is separately and separably fastened to, extends between, and transmits structural loads between, a channel-shaped framing member and one more other structural members, supports or supported objects, which are often similar framing members, thereby tying the framework together. Conversely, the term "fitting" is not customarily applied to non-loadbearing, non-load-transmitting or otherwise adventitious hardware such as springs, nameplates, shims, washers and the like. The fitting is customarily combined with one or more pairs of interengaged threaded members to constitute a fastening for joining loadbearing members of the framework. Some details and examples of typical fittings and fastenings are set forth in the Attwood patent cited hereinabove. In particular, it will be noted that one of the threaded members is elongated in axial cross-section so as to pass through the slot and be rotatable to be able to engage the inside of the slot. This kind of framing system is widely employed because it permits not only rapid and easy construction of support frameworks, but also their ready modification or removal, because the fastenings can be readily moved, removed or changed, the fittings being readily removable from both the framing members and the threaded members when the threaded members are disengaged. It is in this industry-accepted sense that the term "fitting" is employed in this application.
2. Prior Art Problem
The elongated threaded members of such fastenings are generally provided with means, such as protruding corners, which may engage the interior of the channel-shaped member, or grooves which may engage inturned flanges of its slot, for holding the threaded member in the properly rotated position for firmly fastening to the channel-shaped member when a cooperating threaded member is tightly interengaged with the elongated threaded member. However, there is risk that the elongated threaded member may not always be properly rotated to yield a strong and reliable fastening, especially where the parts must be extensively manipulated in a loosened state, or where access or visibility is difficult. Worse, it is difficult to determine by inspection whether the elongated threaded member in an assembled fastening has been properly rotated during assembly, again especially where access or visibility is difficult. Further, there is risk that the elongated threaded member may rotate away from its proper position in a fastening which has become loosened by vibration or racking overstress such as might occur during a seismic event.